One-step constructed dual interfacial layers for stable perovskite solar cells

doi:10.1016/j.mtphys.2022.100796

Materials Today Physics

Volume 27, October 2022, 100796

https://doi.org/10.1016/j.mtphys.2022.100796 Get rights and content

Highlights

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One-step constructed dual interfacial layers of 2D perovskites/PEAI-Spiro simplify the fabrication process of devices.
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The dual interfacial layers effectively suppress interfacial charge-carriers recombination as well as improve hydrophobicity.
•
The solar cells based on dual interfacial layers achieved 10% higher efficiencies compared to control devices.
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The target device retained more than 82% of its initial PCE after 672 h of exposure under 1-sun simulation in ambient air.

Abstract

The highly efficient perovskite solar cells (PSCs) along with excellent long-term stability can be obtained by fabricating two-dimensional (2D) perovskites (PVKs) over the three-dimensional (3D) PVKs film. However, the additional step of forming 2D PVKs before depositing the hole/electron transporting layer would make the device fabrication processes complicated, increasing costs for the manufacture of PSCs. In the present work, 2D PVKs were in-situ formed on surface of the 3D PVKs film by a self-assembly method, together with the deposition of the hole transporting material (HTM) at the same time, which tremendously simplified the fabrication of PSCs based on 3D PVKs/2D PVKs. Based on the one-step constructed 2D PVKs/HTM dual interfacial layers, density of trap states in devices were decreased remarkably owing to efficient interfacial passivation. In the meantime, the hydrophobicity, conductivity and hole extraction ability of the HTM were generally improved, enhancing the operational stability and performance of the solar cells. Thus, the corresponding solar cells increased 10% of average power conversion efficiency, where the highest open circuit voltage is up to 1.174 V. After 672 h of exposure under full 1-sun simulation in ambient conditions, the device still retained more than 82% of its initial PCE which was almost 50% higher than that of the control device.

Graphical abstract

The one-step constructed dual interfacial layers of 2D perovskites/Spiro-OMeTAD contributed to excellent power conversion efficiency and operational stability of perovskite solar cells, which tremendously simplified the fabrication process of devices based on 3D/2D heterojunction perovskites.

Introduction

Despite their modest emergence, organic-inorganic metal halide perovskites (PVKs) with intriguing optoelectronic properties, uncomplicated solution-processability, and low fabrication costs, have become auspicious light-harvesting materials for photovoltaic technologies [[1], [2], [3], [4], [5]]. Nonetheless, plenty of defects at the surface of polycrystalline PVKs films are formed during the deposition and thermal annealing process [[6], [7], [8]], which play as non-radiative recombination centers and thus significantly decrease the photovoltage of devices [9,10]. Therefore, a perovskite solar cell with rather low interfacial defects has already exceeded power conversion efficiency of 25% with a decent open circuit voltage (V_oc) as high as 1.225 V, approximated to the radiative V_oc limit of 1.270 V for single junction solar cells [11]. In addition, defects may initiate the ion migration and moisture permeation into PVKs films, which is the main reason for the prominent hysteresis issue and instability of perovskite solar cells (PSCs) [[12], [13], [14]]. As a result, it is crucial to develop an effective passivation strategy of defects for boosting both the PCE and the long-term stability of PSCs.

Many previous studies demonstrated that the three-dimensional (3D) PVKs/two-dimensional (2D) PVKs heterojunction (i.e. 2D PVKs atop the 3D PVKs film) has been an up-and-coming approach to improve the efficiency and stability of a PSC simultaneously, owing to the decreased density of trap states and hydrophilia of PVKs surface [15]. To date, the most universal method for constructing the 3D PVKs/2D PVKs architecture is through spin-coating organic ammonium salts on surface of the 3D PVKs film where the residual PbI₂ can be reacted to form 2D PVKs [[16], [17], [18], [19], [20]]. However, the solvent, such as isopropyl alcohol (IPA), selected for dissolving most of ammonium salt could unavoidably dissolve the underlying PVKs film due to its relatively high polarity [[21], [22], [23]]. Moreover, an extra thermal treatment is required to accelerate the formation of 2D PVKs materials, which increases both time and energy consuming for the device fabrication process. Thus, it is imperative to develop new strategies of conveniently fabricating high-performance and stable solar cells based on 3D PVKs/2D PVKs.

Here, dual interfacial layers of 2D PVKs/hole transporting materials (HTM) were successfully fabricated by one-step method on the 3D PVKs film, which tremendously simplifies the fabrication of PSCs based on 3D PVKs/2D PVKs. To realize the dual interfacial layers in one step, the Spiro-OMeTAD (2, 2′, 7, 7′-Tetrakis[N, N-di(4-methoxyphenyl)amino]-9, 9′-spirobifluorene) solution added with phenylethylammonium iodide,(C₈H₁₂IN, PEAI) as shown in Fig. S1, was directly spin-coated on surface of the 3D PVKs film. As a result, the hole transporting layer (HTL) of Spiro-OMeTAD was deposited as well as a 2D PVKs layer was in-situ formed by the reaction between organic cations of PEA⁺ from the solution and excess PbI₂ from the surface of the 3D PVKs at the same time. In this process, the high polar solvent like IPA is not used any more, which reduces damage to the 3D PVKs film. With PEAI in the Spiro-OMeTAD, the energy difference between the HTL and the PVKs film was reduced by lowering the highest occupied molecular orbital (HOMO) of the Spiro-OMeTAD from −4.82 to −4.98 eV. The smaller energy difference means the low energy loss during the process of charge transfer between the HTMs and the PVKs film, which is benefit to high V_oc [24,25]. Furthermore, adding PEAI into the Spiro-OMeTAD significantly enhanced the water resistance of the HTMs because of the hydrophobic aromatic group of PEAI, which extended the device lifetime. Compared to control devices, the corresponding target devices exhibited more than 10% enhancement of PCE from 18.64 ± 0.67% to 20.58 ± 0.30%. After 672 h of exposure under full 1-sun illumination in ambient air with a relative humidity (RH) of 35 ± 5% and temperature of 25 ± 5 °C, the target device retained more than 82% of its original PCE, whereas the control device only kept 55% of its original PCE.

Section snippets

Results and discussion

As shown in Fig. 1a, although the UV–Vis absorption spectrum of the Spiro-OMeTAD film added with phenylethylammonium iodide (PEAI-Spiro) shows the same onset to the one that without PEAI (Blank-Spiro), the PEAI-Spiro exhibits a new wide range of strong absorption from 450 to 550 nm as compared to Blank-Spiro which indicates effective oxidization of PEAI-Spiro [26]. The optical bandgap (E_g,opt) of PEAI-Spiro and Blank-Spiro estimated from the Tauc plots were both 3.00 eV, respectively, which

Conclusion

In conclusion, we established a one-step strategy to construct the 2D PVKs/PEAI-Spiro by spin-coating Spiro-OMeTAD added with PEAI on surface of the 3D PVKs film directly, where 2D PVKs were in-situ formed by reacting PEAI with excess PbI₂ from the 3D PVKs film. The one-step fabricated 2D PVKs/PEAI-Spiro dual interfacial layers increased hole extraction and transport, decreased charge-carriers recombination, and enhanced hydrophobicity, which helped improve both the photovoltaic performance and

Materials

Cyclohexane (99.5%), oleic acid (AR), oleylamine (80–90%), tetrabutyl titanate (98.0%), toluene (99.8%), absolute ethanol (99.0%) and 2-propanol (IPA, 99.5%) were purchased from Sigma-Aldrich. N–N dimethylformamide (DMF, ≥99%), dimethyl sulfoxide (DMSO, ≥99%) and chlorobenzene (CB, 99.8%), 4-tert-pyridine (tBP, 98%) Phenethylamine (≥99%), Hydriodic acid (HI, 55–57 wt% solution in H₂O) were purchased from Aladdin. Cesium iodide (CsI, 99.999%), methyl ammonium bromide (MABr, 99.9%), formamidine

Credit author statement

Weihai Sun and Yunlong Li co-conceived and directed the overall project. Fengxian Cao: Investigation, Writing – original draft preparation. Huiwen Chen: Investigation, Visualization. Shibo Wang: Investigation. Pengxu Chen: Investigation. Chenwei Zhu: Investigation. Zhang Lan: Methodology. Weihai Sun: Writing – review & editing. Yunlong Li: Writing – review & editing. Jihuai Wu: Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors thank the Natural Science Foundation of China (Nos. 61804058, U1705256, 21771066 and 51972123), the Young Elite Scientist Sponsorship Program by Cast of China Association for Science and Technology (YESS20210285), the Guangdong Basic and Applied Basic Reuter Foundation (2022A1515011613), and the Promotion Program for Young and Middle-aged Teacher in Science and Technology Research of Huaqiao University (ZQN-706) for financial support.

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¹: F. C. and H. C. contributed equally to this work.

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One-step constructed dual interfacial layers for stable perovskite solar cells

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusion

Materials

Credit author statement

Declaration of competing interest

Acknowledgments

Nano Energy

J. Energy Chem.

Nano Energy

Mater. Today Phys.

Science

Science

Science

Nat. Photonics

Nature

Nat. Photonics

Nat. Energy

Nat. Energy

Adv. Mater. Interfac.

Adv. Mater.

Nature

Nat. Energy

Nat. Energy

Nat. Energy

Adv. Funct. Mater.